Numerous power supply units are known from the prior art.
One difficulty that arises in this context is distinguishing true short circuits from virtual short circuits. Virtual short circuits arise as a result of capacitative loads, which behave like a short circuit, particularly at switch-on. That is, until the capacitative load is appropriately charged, substantial currents can be flowing.
It is for this reason that repeated attempts have been made in the past to identify these virtual short circuits.
For example, an electronic protection device is known from DE 10 2012 103 551 A1 that switches off a controller-controlled switch in dependence on an (output-side) overcurrent and switches it back on again in dependence on the change in voltage at the output. A device that is similar to this is known from DE 10 2013 105 942 A1.
However, the construction of these devices is complicated. In particular, they require an (output-side) current measurement on the basis of which it is decided whether a hazardous state of a true short circuit is present.
It can also be that the supply network cannot supply the current or short-circuit current required for such a detection. Such conditions can occur, for example, when the supply network is already under a heavy load or has a faulty design (e.g., is not powerful enough).
In addition, in the case of weak network components, the voltage can break down dramatically in the event of a short circuit. This can have the effect, for example, that the board supply for the controller (for identifying short circuits and/or controlling the switch) also breaks down, thus rendering the controller unable to respond in the event of a short circuit.
It is therefore the object of the invention to provide an improved and cost-effective power supply unit for the provision of at least one switchable power output that avoids one or more of the drawbacks of the prior art.